Intramembranous Ossification

Chapter 6 Outline

• Cartilage • Bone • Classification and Anatomy of Bones • Ossification • Homeostasis and Bone Growth • Bone Markings • Aging of the Skeletal System Intro to the Skeletal System

• An organ system with tissues that grow and change throughout life – bones – cartilages – ligaments – other supportive connective tissues Cartilage

• Semi-rigid connective tissue – not as strong as bone, more flexible/resilient – mature cartilage is avascular • Cells – ______: produce matrix – ______: surrounded by matrix • live in small spaces called ______Distribution of Cartilage

Figure 6.1 Functions of Cartilage

• Support soft tissues – airways in respiratory system – auricle of ear • ______– smooth surfaces where bones meet • ______model for bone growth – fetal long bones Growth of Cartilage

• Two patterns – ______growth • from inside of the cartilage – ______growth • along outside edge of the cartilage Interstitial Growth

• Mitosis of chondrocytes in lacunae – forms two chondrocytes per lacuna – each synthesize and secrete new matrix – new matrix separates the cells • Result: – larger piece of cartilage – newest cartilage inside Figure 6.2 Appositional Growth

• Mitosis of stem cells in perichondrium – adds chondroblasts to periphery – produce matrix, become chondrocytes – forming new lacunae – adding to existing matrix • Results: – larger piece of cartilage – newest cartilage on outside edges Figure 6.2 Bones

• Living organs containing all four tissue types – primarily connective tissue – extracellular matrix is sturdy and rigid – strengthened by ______: minerals deposited in the matrix (main store and ++ ---) source of Ca and PO4 Function of Bones

• Support • Protection • Movement • Hemopoiesis • Storage Classifying Bones

• ______bones – greater length than width • ______bones – nearly equal length and width • ______bones – thin surfaces • ______bones – other/complex shapes Classification of Bones According to Shape

Figure 6.3 Long Bone Anatomy

• ______– elongated, usually cylindrical, shaft • ______– knobby, enlarged regions at ends – strengthen joints – attachment site for tendons/ligaments • ______– between diaphysis and epiphysis – contains epiphysial (growth) plate Long Bone Anatomy

Figure 6.4 Long Bone Anatomy

• ______cartilage – thin layer of hyaline cartilage on epiphyses – reduces friction between articulating bones • Medullary/marrow cavity – cylindrical space in diaphysis – usually contains yellow bone marrow Long Bone Anatomy

Articular cartilage Spongy bone (contains red Proximal bone marrow) epiphysis Epiphyseal line Metaphysis

Compact bone

Medullary cavity (contains yellow bone marrow in adult) Endosteum

Periosteum

Perforating fibers

Diaphysis Nutrient artery through nutrient foramen

Metaphysis

Epiphyseal line

Distal Figure 6.4 Articular cartilage epiphysis

• ______– dense irregular connective tissue – covers external surfaces of bones • does not cover articular cartilages – acts as anchor for blood vessels and nerves – anchored by perforating fibers embedded in the bone matrix • ______– covers most internal surfaces of bones Bone Coverings

Figure 6.5 Bone Cells

• ______: mesenchymal stem cells, found in endosteum and periosteum, mitotically produce more stem cells or osteoblasts • ______: form bone matrix • ______: reside in lacunae; maintain matrix and communicate with osteoblasts to cause further deposit of bone matrix • ______: large, multinucleate cells that dissolve bone, releasing Ca++ Bone Cells

Figure 6.6 Bone Matrix

• 1/3 organic components – cells – collagen fibers – ground substance • 2/3 inorganic components – bone salt crystals: hydroxyapatite • calcium phosphate and hydroxide

–Ca10(PO4)6(OH)2 Comparing Bone Tissues

• ______bone – solid and relatively dense – external surfaces of long and flat bones • ______bone – open lattice of narrow plates: trabeculae – internal surface of bones Flat Bones

• Have compact and spongy (diploë) bone

Figure 6.7 Compact Bone Organization

• The basic structural and functional unit of mature compact bone is the ______– also known as a ______system – cylindrical structures – parallel to the shaft of the bone Osteon Components

• Canals – ______: carries blood vessels and nerves – ______: perpendicular connections to central canal with blood vessels and nerves – canaliculi: between lacunae allowing metabolic interactions between osteocytes • Lamellae – ______: rings of bone around central canal – ______: along endosteum and periosteum – interstitial: “leftover” pieces of old osteons Osteon or Haversion System

Figure 6.8 Ossification

• The formation and development of bone – also known as osteogenesis – begins by 8th week of embryonic development and continues into adulthood • Two general patterns: – Intramembranous – Endochondral Patterns of Ossification

• Intramembranous ossification – develops from mesenchyme – produces flat bones of the skull, some facial bones, the mandible, and central portion of clavicle • ______ossification – begins with a hyaline cartilage model – produces the majority of bones in the body Stages of Intramembranous Ossification 1. Ossification centers form within thickened regions of mesenchyme

Figure 6.10 Stages of Intramembranous Ossification 2. Osteoid (precursor to solid bone matrix) undergoes calcification

Figure 6.10 Stages of Intramembranous Ossification 3. Woven (primary) bone and surrounding periosteum form

Figure 6.10 Stages of Intramembranous Ossification 4. Lamellar (secondary) bone replaces woven bone as compact and spongy bone form

Figure 6.10 Stages of Endochondral Ossification 1. Fetal hyaline cartilage model develops

Figure 6.11 Stages of Endochondral Ossification 2. Cartilage calcifies and a periosteal bone collar forms around diaphysis

Figure 6.11 Stages of Endochondral Ossification 3. Primary ossification center forms in the diaphysis

Figure 6.11 Stages of Endochondral Ossification 4. Secondary ossification centers form in the epiphysis

Figure 6.11 Stages of Endochondral Ossification 5. Bone replaces cartilage, except the articular cartilage and epiphyseal plates

Figure 6.11 Stages of Endochondral Ossification 6. Epiphyseal plates ossify and form epiphyseal lines

Figure 6.11 The Epiphyseal Plate

• A layer of hyaline cartilage at the boundary of the epiphysis and diaphysis – site of interstitial growth (bone lengthening) – consists of five distinct microscopic zones